1. Field of the Invention
The present invention relates to a program information transport apparatus and a method for transporting program information about digital broadcast programs.
2. Description of the Prior Art
Referring now to FIG. 10, there is illustrated a block diagram showing the structure of a prior art program information transport apparatus. In the figure, reference numeral 1 denotes a PES (Packetized Elementary Stream)/TS (Transport Stream) packetizing unit for packetizing media data such as coded video data, coded audio data, and coded other data so as to generate a plurality of PES streams (each PES is a stream of frames), and for TS-packetizing the plurality of PES streams into a plurality of fixed-length TS packet streams, 2 denotes a memory for storing program information including program specific information (PSI) and the transport cycle time for the program information, 3 denotes a TS packetizing unit for acquiring the program information from the memory 2 at predetermined transport times to start transport of program information, the predetermined transport times being preset based on the transport cycle time, and for packetizing the program information into a stream of TS packets from the acquired program information from the memory 2, and 4 denotes a TS packet multiplexor for multiplexing the TS-packetized media data from the PES/TS packetizing unit 1 and the TS-packetized program information from the TS packetizing unit 3 into a single output stream for transmission, called transport stream (TS).
In operation, in accordance with ITU-T Rec. H.220.0|ISO/IEC 13818-1 (MPEG-2 Systems), the sender of a digital broadcast has to multiplex program specific information PSI and media data into a single output stream. The program specific information PSI is the one needed for receivers to demultiplex the single output stream from the sender into the program information and the media data. The program specific information PSI is divided into four tables including indispensable tables and optional tables. The program specific information PSI is constructed from a program association table or PAT and a program map table or PMT.
When the PES/TS packetizing unit 1 receives media data such as coded video data, coded audio data, and coded other data, it generates PES streams for audio, video, and other data, and after that, generates a plurality of fixed-length TS packet streams from those PES streams so as to transmit the plurality of fixed-length packets over transmission paths. On the other hand, the TS packetizing unit 3 acquires the program information including the program specific information PSI from the memory 2 at the predetermined transport times to start transport of program information (e.g., at predetermined intervals of 100 msec after the packetizing process is started), which are preset based on the transport cycle time for the program information, so as to generate a stream of TS packets from the acquired program information from the memory 2.
After the PES/TS packetizing unit 1 furnishes the plurality of TS-packetized media data streams and the TS packetizing unit 3 furnishes the stream of TS-packetized program information, the TS packet multiplexor 4 multiplexes them into a single output, i.e. a transport stream TS and then sends out the transport stream TS. This technique of multiplexing media data and program information into a single output stream for transmission is disclosed in, for example, Japanese Patent Application Publication (KOKAI) No. 9-284238.
A problem with the prior art program information transport apparatus so constructed as mentioned above is thus that although the prior art apparatus can multiplex program information and media data into a single output stream for transmission, when there is a change in the contents of any one of digital broadcast programs it needs to suspend the process of multiplexing the program information and media data, and then modify the contents of the memory 2 because it cannot accept the change while continuing to perform the process of multiplexing the program information and media data, whereby forcing the multiplexor to suspend the process of multiplexing the program information and media data until the process of modifying the contents of the memory 2 is complete.
The present invention is made to overcome the above problem. It is therefore an object of the present invention to provide a program information transport apparatus and a method for transporting program information about digital broadcast programs, capable of modifying the program information or the like while continuing to perform the process of multiplexing the program information and media data into a single output stream for transmission.
In accordance with one aspect of the present invention, there is provided a program information transport apparatus comprising: a storage unit for storing program information about digital broadcast programs as well as transmission control information including a transport cycle time for the program information; a update unit for accepting a request for a change in either one of the program information and transmission control information stored in the storage unit, and for updating the contents of the storage unit according to the change at predetermined update times to update the program information; an information management unit for acquiring the program information from the storage unit and then furnishing the acquired program information at predetermined transport times to transport the program information, the predetermined transport times being preset based on the transport cycle time stored in the storage unit; and a transport unit for transporting the program information from the information management unit to outside the program information transport apparatus.
Preferably, the transport unit multiplexes the program information from the information management unit and media data into a single output stream, and then transports the single output stream.
The storage unit can store, as the transmission control information, predetermined update times to update the program information, a transport start time to start transport of the program information, a transport end time to finish transport of the program information, and a transport priority assigned to the program information. Further, the update unit can accept a request for a change in either one of the predetermined update times, the transport start time, the transport end time, and the transport priority, which are stored in the storage unit.
Preferably, the information management unit starts to transfer the program information to the transport unit after the transport start time for the program information.
Preferably, the information management unit can also finish transferring the program information to the transport unit after the transport end time for the program information. The information management unit can also erase the program information from the storage unit after the transport end time for the program information.
Preferably, the storage unit stores a plurality of pieces of program information, the information management unit sequentially transfers the plurality of pieces of program information to the transport unit in order of transport priority if some of the plurality of pieces of program information have to be transported at the same transport times.
In accordance with a preferred embodiment of the present invention, the program information transport apparatus further includes an extracting unit for extracting program information from multiplexed data, into which media data and the program information are multiplexed, transported thereto from outside the apparatus. Further, the storage unit can further store program information that is the same as program information previously-extracted by the extracting unit until the extracting means extracts the current program information. The storage unit can also store a transport cycle time for the program information. The program information transport apparatus can further include a second update unit for determining whether or not there is a change in the extracted program information by comparing the extracted program information with the previous program information stored in the storage unit, and for updating the contents of the storage unit according to the program information extracted by the extracting unit only if there is a change in the extracted program information. The information management unit also acquires the program information from the storage unit and then furnishes the acquired program information to the transport unit at predetermined transport times to transport the program information, the predetermined transport times being preset based on the transport cycle time stored in the storage unit.
In accordance with another aspect of the present invention, there is provided a program information transport apparatus comprising: an extracting unit for extracting program information from multiplexed data, into which media data and the program information are multiplexed, transported thereto from outside the apparatus; a storage unit for storing program information, which is the same as previously-extracted program information, until the extracting means extracts the current program information, and for storing a transport cycle time for the program information; a update unit for determining whether or not there is a change in the program information extracted by the extracting unit by comparing the extracted program information with the previous program information stored in the storage unit, and for updating the previous program information stored in the storage unit according to the program information extracted by the extracting unit, only if there is a change in the extracted program information; an information management unit for acquiring the program information from the storage unit and then furnishing the acquired program information at predetermined transport times to transport the program information, the predetermined transport times being preset based on the transport cycle time; and a transport unit for transporting the program information transferred thereto from the information management unit to outside the program information transport apparatus.
In accordance with another aspect of the present invention, there is provided a method of transporting program information, comprising the steps of: prestoring program information about digital broadcast programs and transmission control information including a transport cycle time for the program information in a memory; accepting a request for a change in either one of the program information and the transmission control information stored in the memory; updating the contents of the memory according to the change at predetermined update times to update the program information; acquiring the program information from the memory and then multiplexing the acquired program information and media data into an output stream at predetermined transport times to transport the program information, the predetermined transport times being preset based on the transport cycle time; and transporting the output stream to outside.
In accordance with another aspect of the present invention, there is provided a method of transporting program information transport, comprising the steps of: extracting program information from multiplexed data, into which media data and the program information are multiplexed, transported thereto from outside, storing program information, which is the same as previously-extracted program information, in a memory until the current program information is extracted from the multiplexed data, and storing a transport cycle time for the program information in the memory; determining whether or not there is a change in the program information by comparing the extracted program information with the previous program information; updating the contents of the memory according to the extracted program information, only if there is a change in the program information; acquiring the program information from the memory and then furnishing the acquired program information at predetermined transport times to transport the program information, the predetermined transport times being preset based on the transport cycle time; and transporting the program information to outside.